My daschund started shaking with mouth open and can't shut mouth during this. When stop shaking, the mouth doesn't close right. What could be the cause of this?

Ma'am you really need to take your dog to the vet. It may be one of many things a seizure, stroke, allergic reaction.. only a vet could tell you.

These things always happen on a weekend. While it is fresh in your mind write down all the details. Even after examining the dog, the vet may or may not be able to say what caused it or how to prevent future problems. So get it to the vet next week and hope for the best. You should seek emergency care if it has another such spell before then.